Bolivia

New drainage works protect lives and homes in La Paz

Construction or repairs of more than 5,400 meters of drainage works being carried out in the Bolivian city of La Paz with IDB support are helping to prevent landslides, erosion, and material and human losses.

During and immediately after the rainy season the city suffers collapses in its drainage system due to its small capacity. Improvements in the system, especially in the old neighborhoods, will prevent flooding and protect inhabitants, and improve quality of life.

The La Paz Storm Drainage Program is being financed with a loan for $22 million extended from the IDB’s Fund for Special Operations in 2007.

Improving the social environment

La Paz’s very complex geological, geotechnical, hydrological, and topographical conditions make maintenance of the city’s urban infrastructure difficult and subject to natural events such as floods and landslides. Limited urban area for expansion results in unregulated squatting on geologically unstable and steep hillsides cousing an accumulation of sediment and garbage that blocks drainage channels and pipes. During the November through February rainy season, drainage problems result in overflows, floods, main sewer collapses, landslides, and slope destabilization that take lives and damage and destroy buildings.

The problems stem from a number of factors: lack of comprehensive planning, deterioration and/or collapse of drainage works, uncontrolled urban growth, lack of sediment control, unregulated dumping of solid waste and inadequate street cleaning, and insufficient maintenance of hydraulic works. The city’s sanitary sewage system and storm drainage system operate separately in a secondary network, but converge in the main sewers, which open directly into the rivers. As a result, the waterways are highly polluted, especially in times of low rainfall.

In the north of the city, the main drainage system of the Choqueyapu and Orkojahuira watersheds is comprised of very old open and vaulted sewers. Due to the high speed of runoff and the resulting erosion, many conduits in these watersheds are in poor shape, preventing their use during heavy rains when the need is greatest. In the southern watersheds of the Irpavi, Achumani, and Huayñajahuira rivers, the drainage system is largely comprised of open sewers; during the rainy season, large quantities of solid granular material collects in the drainage structures and causes flooding.

In 2003, the La Paz Storm Drainage Master Plan (PMDP) was updated with the support of an IDB grant financed by the Japanese Trust Fund. The plan, which sets forth both structural and nonstructural actions in all the city’s watersheds up to 2025, forms the basis for the present Bank operation. Subsequent IDB grants financed a diagnostic assessment of storm drainage system management and costs and detailed designs for short-term investments and their respective environmental, social, and economic impacts.

The program in brief

The La Paz Storm Drainage Program is financing works identified in the PMDP in the city’s five main watersheds, each of which presents different challenges.

Macrodrainage works include improvement and rehabilitation of vaults and sewers and new drainage works. Smaller works are controlling surface runoff by rehabilitating existing drains and building new ones.

Works and complementary actions include measures to protect the drainage system, including structures to reduce water erosion and promote reforestation in the upper watershed, sediment retention works in the upper and middle sections of the watershed, and implementation of a disaster risk prevention plan and an environmental education and citizen participation program to instill the need for proper garbage disposal and improved land use. In addition, studies are being prepared for future works identified in the PMDP.

The program also includes support for improving urban management and planning related to the La Paz storm water drainage system and urban growth to ensure sustainability of the investments, particularly operation and maintenance. Specific areas for support include study and implementation of a preventive maintenance plan for the drainage system; a study to supplement the macrodrainage system cadastre; procurement of equipment for maintaining the macrodrainage system; support for the Chief Administrative Office for Land Management for carrying out land management actions in the La Paz River basin, in particular the Ecological-Territorial Management Plan for Land Use in La Paz Urban Watersheds; and support for a study on optimizing the street cleaning system in core areas of La Paz that generate large quantities of solid waste through the provision of necessary equipment.

Toward the future

The program is part of a long-term process in a vulnerable city that needs to improve its drainage system based on a master plan designed to address problems resulting from its landscape, rain regime, geology, and particularly rapid growth in population that often takes place chaotically and with few controls. Experiences gained in La Paz on social and natural risk mitigation and control are applied in Bolivia’s other cities.